are pretty neutral last I checked. But weren't they rumored to be extinct by the 23-24th century?
There was some talk by ENT's producers that we eventually would know why we don't see any Suliban in TOS and TNG, but ultimately the Suliban were an idea that was dropped much like the Kazon in VOY.
For all we know, though, the Suliban are still around in the 24th-Century, but with the Galaxy being such a big place, it's not implausible that our heroes tend to be in places the Suliban aren't. Other Starfleet crews might deal with them more regularly, however.